Friction stir welding (FSW) is a solid-state process for joining two bodies. In FSW, a welding end of a pin tool assembly is rotated, brought into contact with the two bodies at a joint therebetween, and plunged into the two bodies. This generates heat due to friction between the welding end of the pin tool assembly and the two bodies, which softens the two bodies. Rotation of the welding end then causes mixing of the materials that form the two bodies. The pin tool assembly may be translated along the joint, thereby joining, or welding, the two bodies at the joint.
The welding end may be fixed relative to a remainder of the pin tool assembly (but still rotated relative to the two bodies). Under these conditions, friction stir welding of the two bodies leaves a void space, or divot, at the end of a weld therebetween. This may be especially true when the joint is a circumferential joint. Alternatively, the welding end of the pin tool assembly may be configured to retract into the pin tool assembly, thereby controlling and/or regulating a depth of penetration of the welding end into the two bodies during friction stir welding of the two bodies. This permits the pin tool assembly to weld materials of different and/or varying thickness (e.g., thicknesses that vary along a length of the joint). Additionally or alternatively, this also permits the welding end to be retracted at the end of a weld between the two bodies, thereby permitting termination of the weld without leaving the void space.
While pin tool assemblies with retractable welding ends may be effective at friction stir welding various bodies together, it may be difficult to accurately control and/or regulate the extent to which the welding end extends from and/or is retracted into the pin tool assembly, especially when the pin tool assembly is subjected to the high applied forces that often are utilized in friction stir welding. Thus, there exists a need for improved pin tool assemblies for friction stir welding and/or for friction stir welding apparatus and/or methods that include the improved pin tool assemblies.